public class MsgBox : System.Windows.Forms.Form
    {
        Label bodyLabel = new Label();        
        Button yesBtn = new Button();
        Button noBtn = new Button();
        public MsgBox()
        {
        }

        public MsgBox(string titleMsg, string bodyMsg, string yesMsg,string noMsg)
        {             
            
 
this.ClientSize = new System.Drawing.Size(490, 150);
            this.Text = titleMsg;            

            yesBtn.Location = new System.Drawing.Point(111, 112);
            yesBtn.Size = new System.Drawing.Size(75, 23);
            yesBtn.Text = yesMsg;
            yesBtn.BackColor = Control.DefaultBackColor;
            yesBtn.Click 
 
+= YesBtnClick;

            noBtn.Location = new System.Drawing.Point(311, 112);
            noBtn.Size = new System.Drawing.Size(75, 23);
            noBtn.Text = noMsg;
            noBtn.BackColor = Control.DefaultBackColor;
            noBtn.Click += NoBtnClick;

            bodyLabel.Location = new
 
 System.Drawing.Point(111, 50);
            bodyLabel.Text = bodyMsg;
            bodyLabel.Font = Control.DefaultFont;
            bodyLabel.AutoSize = true;

            this.BackColor = Color.White;
            this.ShowIcon = false;

            this.Controls.Add(noBtn);
            this.Controls.Add(yesBtn);
            this.Controls.Add(bodyLabel);
        }

      

        private void YesBtnClick(object sender, EventArgs e)
        {
            this.DialogResult = DialogResult.Yes;
        }

        private void NoBtnClick(object sender, EventArgs e)
        {
            this.DialogResult = DialogResult.No;
        }
    }

 static void CustomizeMsgBoxDemo()
        {
            MsgBox msgBoxForm = new MsgBox(
            "Warning",
            "Is it right!",
            "Right!",
            "Wrong!"
            );
            msgBoxForm.FormBorderStyle = FormBorderStyle.FixedSingle;
            msgBoxForm.MaximizeBox = false;
            msgBoxForm.MinimizeBox = false;
            msgBoxForm.StartPosition = FormStartPosition.CenterParent;
            DialogResult dlgResult=msgBoxForm.ShowDialog();
            if(dlgResult==DialogResult.Yes)
            {
                MessageBox.Show("Right!");
            }
            else
            {
                MessageBox.Show("Wrong!");
            }
        }

Copy and update from

https://stackoverflow.com/questions/12704026/how-to-change-text-on-messagebox-buttons